Double Displacement Reaction: \(K_2SO_4\) and \(BaCl_2\)

The provided chemical reaction is:

\(K_2SO_4 \text{ (aq.)} + BaCl_2 \text{ (aq.)} \rightarrow 2KCl \text{ (aq.)} + BaSO_4\downarrow \text{ (solid)}\)

Let's analyze this reaction to understand why it is classified as a double displacement reaction.

Understanding the Reaction Mechanism

In this reaction, we start with two ionic compounds dissolved in water:

• Potassium sulfate (\(K_2SO_4\))
• Barium chloride (\(BaCl_2\))

When these two aqueous solutions are mixed, the ions present are \(K^+\), \(SO_4^{2-}\), \(Ba^{2+}\), and \(Cl^-\). In a double displacement reaction, the positive ions (cations) and negative ions (anions) of the two reactant compounds switch partners.

• The cation from the first compound (\(K^+\)) combines with the anion from the second compound (\(Cl^-\)).
• The cation from the second compound (\(Ba^{2+}\)) combines with the anion from the first compound (\(SO_4^{2-}\)).

This results in the formation of two new compounds:

• Potassium chloride (\(KCl\)), which remains dissolved in water (aqueous, aq.).
• Barium sulfate (\(BaSO_4\)), which is insoluble in water and forms a solid precipitate (\(\downarrow\), solid).

The overall process involves the exchange of ions: the \(K^+\) ions were initially with \(SO_4^{2-}\) and the \(Ba^{2+}\) ions were with \(Cl^-\). After the reaction, \(K^+\) ions are with \(Cl^-\) and \(Ba^{2+}\) ions are with \(SO_4^{2-}\). This characteristic exchange defines it as a double displacement reaction.

Comparing with Other Reaction Types

Let's see why the other options are not suitable:

• Addition reaction: In an addition reaction, two or more simple substances combine to form a single, more complex product. This reaction produces two products (\(KCl\) and \(BaSO_4\)), so it is not an addition reaction.
• Displacement reaction: A displacement reaction typically involves a more reactive element displacing a less reactive element from its compound (e.g., \(Zn + CuSO_4 \rightarrow ZnSO_4 + Cu\)). In this reaction, ions are swapping places, not a single element displacing another.
• Decomposition reaction: A decomposition reaction occurs when a single compound breaks down into two or more simpler substances (e.g., \(CaCO_3 \rightarrow CaO + CO_2\)). This reaction involves two reactants combining and rearranging, not breaking down.
• Double displacement reaction: This perfectly describes the reaction where the ions \(K^+\) and \(Ba^{2+}\) switch their respective partners \(SO_4^{2-}\) and \(Cl^-\), leading to the formation of new compounds, one of which is a precipitate.

Conclusion

The reaction \(K_2SO_4 \text{ (aq.)} + BaCl_2 \text{ (aq.)} \rightarrow 2KCl \text{ (aq.)} + BaSO_4\downarrow \text{ (solid)}\) is a clear example of a double displacement reaction because the cations (\(K^+\) and \(Ba^{2+}\)) and anions (\(SO_4^{2-}\) and \(Cl^-\)) exchange partners between the two reacting ionic compounds.